(1) Field of the Invention
The present invention relates to a method and apparatus for false twisting yarns by using a false twisting element including a set of 4 shafts, each shaft having at least one rotary frictional disc mounted thereon, and passing two running yarns through this false twisting element to impart false twists thereto.
(2) Description of the Prior Art
As the conventional false twisting method and apparatus, there can be mentioned so-called three-shaft false twisting method and apparatus in which one running yarn is passed through a false twisting element including a set of three shafts and frictional discs mounted on the three shafts so that they partially overlap one another.
According to this conventional false twisting technique, since only one yarn is processed by one false twisting element, the production efficiency is not sufficient, especially when large denier false twisted yarns are prepared. Moreover, crimp characteristics of the resulting processed yarns are not satisfactory.
The specification of British Patent No. 1,419,086 proposes a false twisting element comprising a set of 4 shafts, each including a rotary frictional disc mounted thereon. As illustrated in the specification, in this false twisting element, discs 11 and 11a are disposed at the same height. Accordingly, when two yarns are false twisted by passing them through this false twisting element, for the reasons set forth hereinafter, it is very difficult to false twist the two yarns under the substantially same processing conditions.
FIG. 1 illustrates the state of contact between a frictional disc and a yarn. In the case where a yarn 3 is not passed through a region defined by an angle 0 between the rotational direction of a frictional disc 1 and a rotational shaft 2 as shown in FIG. 1-A, the frictional force F imposed on the yarn 3 by the frictional disc 1 is divided into components f.sub.1 and f.sub.2. The direction of the component f.sub.1 is opposite to the direction of advance of the yarn 3 indicated by arrow 3'. Accordingly, this component f.sub.1 of the force acts on the yarn 3 so that the advance of the yarn 3 in the direction 3' is inhibited. This means that a large tension is imposed on the yarn 3 at the false twisting step and the yarn 3 is not easily delivered. Accordingly, in the state shown in FIG. 1-A, it is impossible to process yarns satisfactorily. In this case, the component f.sub.2 of the force acts as a force of twisting yarns.
In the state shown in FIG. 1-B, the yarn 3 advances at a certain angle .alpha. through a region defined by an angle 0 between the rotational direction of a frictional disc 1 and a rotational shaft 2. The direction of the component f.sub.1 of the frictional force F is the same as the direction of advance of the yarn 3 indicated by arrow 3'. In this case, delivery of the yarn 3 is expedited and no abnormal tension is imposed on the yarn 3. Accordingly, in this case, the yarn can be false twisted under good conditions.
In the above-mentioned false twisting element disclosed in the specification of British Patent No. 1,419,086, since two of the four frictional discs are set at the same height in four rotational shafts, if two yarns are simultaneously fed into this false twisting element, one of the two yarns is inevitably processed in the state shown in FIG. 1-A. More specifically, a force acting in the advance direction of the yarn is imposed on one yarn (the state shown in FIG. 1-B), but a force acting in a direction opposite to the yarn advance direction is imposed on the other yarn (the state shown in FIG. 1-A). In case of the yarn on which the force acting in the direction opposite to the yarn advance direction, even setting of the yarn to the false twisting apparatus is very difficult, and if the yarn is set, there are brought about considerble differences of the yarn tension (twisting or untwisting tension), twist number and the like factors between the two yarns during processing. Therefore, it is impossible to process the two yarns substantially under the same conditions. Further, depending on the quality of yarns to be processed or under some processing conditions, yarn breakage and other troubles take place and it is impossible to perform the operation stably.
As will be apparent from the foregoing illustration, in the known 4-shaft outer-contact type false twisting apparatus, the disc-yarn contact angle differs greatly between the two yarns to be processed, and therefore, the quality differs in the two yarns and one of the two yarns is not substantially even false twisted. Accordingly, such conventional false twisting apparatus can hardly be applied to a practical yarn manufacturing line.
Therefore, it has been desired in the art that the false twisting method using the above-mentioned outer-contact type false twisting apparatus will be improved so that two yarns to be processed can be false twisted simultaneously under the condition shown in FIG. 1-B and properties of both the two yarns can be made uniform or changed according to need.